DNA immunizations with M2 muscarinic and beta1 adrenergic receptor coding plasmids impair cardiac function in mice

Autoimmune mediated myocardial damage is likely to be a pathogenic mechanism for acquired dilated cardiomyopathies. Evidence confirms that autoantibodies that bind to M(2) muscarinic (M(2)AChR) and beta(1) adrenergic receptors (beta(1)AR) are present in idiopathic dilated cardiomyopathy and Chagasic patients' sera. To elucidate the role of these antibodies in cardiac functional impairment, we used a murine model immunized with plasmids encoding the M(2)AChR or beta(1)AR via gene-gun bombardment. Anti-M(2)AChR and beta(1)AR antibodies were detected over the course of 37 weeks. These antibodies were directed to the second extracellular loop (el2) of both receptors and the third intracellular loop (il3) of the M(2)AChR. Peak antibody titers from weeks 2 to 5 against M(2)AChR-el2 and beta(1)AR-el2 as well as elevated titers against M(2)AChR-il3 were detected. Anti-M(2)AChR-il3 and anti-beta(1)AR-el2 antibodies were predominant in IgG1 subclass immunoglobulins, suggesting a T-helper-2 biased lymphocyte response. Heart morphology and function was assessed by echocardiography over the course of 42 weeks. Data showed progressive decrease in left ventricular (LV) wall thickness and LV mass that was mostly evident for beta(1)AR-immunized mice albeit a small change in LV dimensions. Fractional shortening was altered and values of 41%, 37% and 48% were observed at week 42 for the M(2)AChR, beta(1)AR and control groups respectively. In support of autonomic deregulation, a twofold increase in M(2)AChR and a similar decrease in beta(1)AR density were observed in radioligand saturation assays for both experimental groups. Histological analysis revealed myofibril disarray and fibrosis, pointing towards remodeling as a consequence of the long-term presence of anti-receptor antibodies.     

抗β1-肾上腺素受体抗体对大鼠T淋巴细胞的作用

目的观察抗β1-肾上腺素受体（AR）抗体对大鼠T淋巴细胞的作用。方法用人工合成的β1-肾上腺素受体细胞外第二环肽段（β1-AR—ECⅡ）作为抗原主动免疫大鼠,采用流式细胞技术测定大鼠外周血T淋巴细胞亚群的变化;观察抗β1-AR自身抗体对培养的淋巴结T细胞的影响。结果免疫组血清中T淋巴细胞亚群CD4^＋／CD8^＋在处理24h后开始升高,在第7天时达到高峰并持续2个月;抗β1-AR自身抗体可促进T淋巴细胞增殖,与β1-AR特异性阻断剂Metoprolol或β1-AR—ECⅡ共同作用时,可使抗体的促增殖效能显著减弱。结论抗β1-AR自身抗体可以使免疫系统失衡,促进T淋巴细胞的增殖。     

β1受体自身抗体和美托洛尔对糖尿病高血压患者并发心力衰竭的影响

目的观察β1受体自身抗体（β1R-AAb）阳性的糖尿病合并β1力衰竭患者β受体阻滞剂靶向治疗对心功能的疗效。方法（1）以合成的8。受体多肽片段为抗原,应用ELISA法检测三组的β1R-AAb：糖尿病合并高血压心力衰竭患者96例（DM＋HT＋CF组）,糖尿病合并高血压无心力衰竭患者60例（DM＋HT组）,正常对照60名（NC组）。（2）DM＋HT＋CF组分为β1R—AAb阳性者51例（β1R—AAb＋组）和β1R-AAb阴性者45例（β1R-AAb-组）。两亚组均给予：培哚普利4mg,日1次;尼群地平10mg,6小时1次;氢氯噻嗪12．5mg,日1次;阿司匹林100mg,日1次;硝酸异山梨醇酯10mg,日3次;地高辛12．5mg,日1次;酒石酸美托洛尔25mg,日2次。疗程为3～6个月。（3）超声心动图对比观察该治疗方案对心功能的疗效。结果（1）DM＋HT＋CF组β1R-AAb阳性率（53．1％）明显高于DM＋HT组（11．7％）及NC组（8．3％）,P均〈0．01。（2）β1R-AAb＋组收缩功能改善明显优于β1R-AAb-组（P〈0．01）。（3）临床降压效果评定,甩R-AAb＋组总有效率（88．2％）,明显高于目R-AAb-组（51．1％）,P〈0．01。结论对DM合并高血压心力衰竭患者,通过β1受体自身抗体检测,对阳性者有针对性地选择酒石酸美托洛尔,可明显改善糖尿病患者心功能且较安全。     

Autoimmunity against the second extracellular loop of beta(1)-adrenergic receptors induces beta-adrenergic receptor desensitization and myocardial hypertrophy in vivo

Although immunoapheresis removing autoantibodies against the second extracellular domain of beta(1)-adrenergic receptors (ARs) improves cardiac function in patients with cardiomyopathy, the underlying mechanisms have not been defined. We examined the role of autoimmunity against the domain in the development of cardiac dysfunction in vivo. Japanese white rabbits were immunized with a synthetic peptide corresponding to the second extracellular loop of beta(1)-AR once a month with (beta+biso rabbits, n=10) or without (beta rabbits, n=13) bisoprolol treatment (2 mg/kg per day). Control rabbits received vehicle without bisoprolol treatment (n=13). Autoantibodies of IgG isotype against the domain were persistently detected in beta and beta+biso rabbits. Purified IgG from sera of beta and beta+biso rabbits increased cAMP production in a rabbit cardiac membrane preparation, which was blocked by bisoprolol. At 3 months, beta-AR uncoupling with increased G protein-coupled receptor kinase 5 (GRK5) expression was found in beta rabbits. At 6 months, left ventricular hypertrophy was noted with hemodynamic derangements in beta rabbits. This was accompanied by decreased beta(1)-AR density and increased inhibitory G protein and GRK5 expression, which were related to marked decrease in membrane cAMP production. These changes in beta rabbits at 6 months were prevented in beta+biso rabbits. There was no difference in the plasma norepinephrine concentration in the 3 groups over the observation period. Thus, autoimmunity against the second extracellular loop of beta(1)-ARs induced profound beta-AR desensitization and myocardial hypertrophy in vivo, associated with cardiac dysfunction. Sustained sympathomimetic-like actions of autoantibodies against the domain may be partly responsible for these changes.     

Autoimmunity against the second extracellular loop of beta(1)-adrenergic receptors induces early afterdepolarization and decreases in K-channel density in rabbits

OBJECTIVES: We sought to define the electrophysiologic property of the rabbit heart associated with autoimmunity against the second extracellular loop of the beta(1)-adrenergic receptor. BACKGROUND: Sudden death of patients with cardiomyopathy, probably due to lethal ventricular arrhythmias, can be predicted by the presence of autoantibodies against the second extracellular loop of the beta(1)-adrenergic receptor. METHODS: Rabbits were immunized by repetitive subcutaneous administration of a synthetic peptide corresponding to the second extracellular loop of beta(1)-adrenergic receptors (beta group; n = 30) for a mean of 4.2 months. Control rabbits received only vehicle (control group; n = 30). RESULTS: One of the rabbits in the beta group died suddenly during the observation period, but none of the control animals died. The prevalence of sustained ventricular tachycardia was significantly higher in the beta group (beta: 4 of 27 vs. control: 0 of 30), and a standard microelectrode experiment revealed prolongation of the action potential duration (APD) in the right ventricular papillary muscle (beta: 156 +/- 5 ms vs. control: 131 +/- 4 ms; p < 0.05). Early afterdepolarization (EAD) was observed in one rabbit in the beta group (1 of 26), but not in any animals in the control group (0 of 17). A dose of 100 nmol/l of E-4031 induced EAD in the beta group (10 of 10), but not in the control group, except for one rabbit (1 of 10). The whole-cell, patch-clamp experiment on left ventricular M cells showed significant decreases in transient outward current (I(to1)) (-43%) and slowly activated delayed rectifier current (I(Ks)) densities (-33%), whereas the inward-rectifying K current (I(K1)) and rapidly activated delayed rectifier current (I(Kr)) densities remained unchanged. CONCLUSIONS: Long-term immunization against the second extracellular loop of the beta(1)-adrenergic receptor caused EAD and APD prolongation and decreased the K-channel density, suggesting that an arrhythmic substrate via autoimmune mechanisms is present in cardiomyopathic patients who have autoantibodies directed against the receptors.     

Detection of Anti-β1-AR Autoantibodies in Heart Failure by a Cell-Based Competition ELISA

Rationale: Autoantibodies directed against the second extracellular loop of the cardiac β1-adrenergic receptor (β1-AR) are thought to contribute to the pathogenesis of dilated cardiomyopathy (DCM) and Chagas heart disease. Various approaches have been used to detect such autoantibodies; however, the reported prevalence varies largely, depending on the detection method used. Objective: We analyzed sera from 167 DCM patients (ejection fraction <45%) and from 110 age-matched volunteers who did not report any heart disease themselves, with an often used simple peptide-ELISA approach, and compared it with a novel whole cell-based ELISA, using cells expressing the full transgene for the human β1-AR. Additionally, 35 patients with hypertensive heart disease with preserved ejection fraction were investigated. Methods and Results: The novel assay was designed according to the currently most reliable anti-TSH receptor antibody-ELISA used to diagnose Graves disease ("third-generation assay") and also detects the target antibodies by competition with a specific monoclonal anti-β1-AR antibody (β1-AR MAb) directed against the functionally relevant β1-AR epitope. Anti-β1-AR antibodies were detected in ≈60% of DCM patients and in ≈8% of healthy volunteers using the same cutoff values. The prevalence of these antibodies was 17% in patients with hypertensive heart disease. Anti-β1-AR antibody titers (defined as inhibition of β1-AR MAb-binding) were no longer detected after depleting sera from IgG antibodies by protein G adsorption. In contrast, a previously used ELISA conducted with a linear 26-meric peptide derived from the second extracellular β1-AR loop yielded a high number of false-positive results precluding any specific identification of DCM patients. Conclusions: We established a simple and efficient screening assay detecting disease-relevant β1-AR autoantibodies in patient sera yielding a high reproducibility also in high throughput screening. The assay was validated according to "good laboratory practice" and can serve as a companion biodiagnostic assay for the development and evaluation of antibody-directed therapies in antibody-positive heart failure.     

Beta-blockers alprenolol and carvedilol stimulate beta-arrestin-mediated EGFR transactivation

Recent evidence suggests that binding of agonist to its cognate receptor initiates not only classical G protein-mediated signaling, but also beta-arrestin-dependent signaling. One such beta-arrestin-mediated pathway uses the beta(1)-adrenergic receptor (beta(1)AR) to transactivate the EGFR. To determine whether beta-adrenergic ligands that do not activate G protein signaling (i.e., beta-blockers) can stabilize the beta(1)AR in a signaling conformation, we screened 20 beta-blockers for their ability to stimulate beta-arrestin-mediated EGFR transactivation. Here we show that only alprenolol (Alp) and carvedilol (Car) induce beta(1)AR-mediated transactivation of the EGFR and downstream ERK activation. By using mutants of the beta(1)AR lacking G protein-coupled receptor kinase phosphorylation sites and siRNA directed against beta-arrestin, we show that Alp- and Car-stimulated EGFR transactivation requires beta(1)AR phosphorylation at consensus G protein-coupled receptor kinase sites and beta-arrestin recruitment to the ligand-occupied receptor. Moreover, pharmacological inhibition of Src and EGFR blocked Alp- and Car-stimulated EGFR transactivation. Our findings demonstrate that Alp and Car are ligands that not only act as classical receptor antagonists, but can also stimulate signaling pathways in a G protein-independent, beta-arrestin-dependent fashion.     

血管紧张素Ⅱ1型受体胞外第二环肽抗体对大鼠血管平滑肌细胞质游离钙水平的影响

目的观察血管紧张素Ⅱ1型受体(AT1受体)细胞外第二环肽抗体对培养大鼠主动脉血管平滑肌细胞(VSMC)细胞质游离钙水平的影响。方法采用酶联免疫吸附测定法检测高血压患者血清中抗AT1受体抗体,亲和层析法提取阳性血清中的AT1受体细胞外第二环肽抗体。同时应用AT1受体胞外第二环肽主动免疫大鼠并提取抗体。将血管紧张素Ⅱ(AngⅡ),患者及大鼠的AT1受体胞外二环肽抗体分别刺激钙离子荧光探针Fluo-3/AM负载培养原代大鼠VSMC,观察荧光强度变化来检测细胞质游离钙水平变化。结果患者及大鼠血清中提取的AT1受体第二环肽抗体均刺激培养VSMC使细胞质游离钙水平升高,作用与AngⅡ类似。进一步实验发现抗体的激动效应能够被AT1受体胞外第二环肽的抗原表位序列及AT1受体拮抗剂氯沙坦阻断。结论针对AT1受体胞外第二环肽抗体具备激动效应,通过激动AT1受体刺激细胞质钙离子浓度增高,提示该抗体在高血压发病机制中起重要作用。     

糖尿病患者血清抗AT1和α1肾上腺素能受体自身抗体与白蛋白尿的关系

目的探讨糖尿病（DM）患者血管紧张素Ⅱ受体1（AT1受体）和α1肾上腺素能受体（α1受体）自身抗体与白蛋白尿的关系。方法以合成的AT1和α1受体多肽片段为抗原,应用酶联免疫吸附技术,检测171例糖尿病患者（DM组）、60例高血压无肾损患者（HT组）及40例正常人（NC组）血清中抗AT1和α1受体自身抗体及尿白蛋白排泄率（UAER）。DM组根据UAER分为DM1组（UAER≥200μg／min）;DM2组（UAER为20-199μg／min）;DM3组（UAER＜20μg／min）。结果（1）DM组抗AT1和α1受体抗体阳性率分别为53．2％和56．1％,明显高于HT组的13．3％和15．0％及NC组的12．5％和7．5％,差异有统计学意义（P均〈0．01）。（2）DM1组抗AT1和α1受体自身抗体阳性率分别为83．6％和82．O％,明显高于DM2组的66．0％和62．5％及DM3组的11．7％和8．3％,差异有统计学意义（P均〈0．01）,DM2组明显高于DM3组（P〈0．01）。结论血清抗G蛋白偶联型AT1和α1受体自身抗体可能与DM合并肾损害有关,AT1和α1受体自身抗体阳性率与白蛋白尿有关。AT1和α1受体自身抗体在DM合并肾损害发病中起重要作用。     

Modulation of beta1-adrenoceptor activity by domain-specific antibodies and heart failure-associated autoantibodies

OBJECTIVES: Our study attempted to gain further understanding of the allosteric effects of human autoantibodies on beta1-adrenergic receptor (beta1-AR) function. BACKGROUND: Recently, we reported on the existence of activating anti-beta1-AR antibodies in patients with dilated cardiomyopathy (DCM 26% prevalence) or ischemic cardiomyopathy (ICM, 10% prevalence); however, their functional effects have not yet been thoroughly characterized. METHODS: In this study we detected functionally active receptor-antibodies in 8 out of 30 DCM patients. Their immunological and functional properties were analyzed using both synthetic receptor-peptides and intact recombinant human beta1-AR, and were compared with those of heterologous antibodies to selected beta1-AR domains generated in rabbits and mice. RESULTS: Rabbit, mouse, and human anti-beta1-AR against the second extracellular domain preferentially bound to a native receptor conformation and impaired radioligand binding to the receptor. However, their functional effects differed considerably: Rabbit and mouse antibodies decreased both basal and agonist-stimulated cAMP production, whereas the patient antibodies (n = 8) increased basal, and six of them also increased agonist-stimulated receptor activity (i.e., acted as receptor-sensitizing agents). Two out of eight human anti-beta1-AR increased basal but decreased agonist-stimulated receptor activity (i.e., acted as partial agonists). CONCLUSIONS: Antibodies against the same small beta1-AR domain can have very divergent allosteric effects, ranging from inhibitory to agonist-promoting activities. Activating autoantibodies were associated with severe cardiac dysfunction and thus might be involved in the development and/or course of human cardiomyopathy.     

Active immunization of combined beta1-adrenoceptor and M2-muscarinic receptor peptides induces cardiac hypertrophy in rabbits.

BACKGROUND: The high prevalence of patients with dilated cardiomyopathy (DCM) with anti-beta1-adrenoceptor and/or anti-M2-muscarinic receptor autoantibodies in their sera has been observed. However, the pathophysiological role of these autoantibodies in the development of cardiomyopathy is unknown. We previously reported an experimental model of early-stage DCM-like cardiomyopathy induced by immunizing rabbits for 1 year with synthetic peptides corresponding to the sequence of the second extracellular loop of either beta1-adrenoceptor or M2-muscarinic receptor. Because approximately half the sera of patients with DCM that recognize one of the two receptor sequences also recognize the second sequence, a model was created in rabbits simultaneously immunized with the synthetic peptides corresponding to the second extracellular loop of the beta1-adrenoceptor and M2-muscarinic receptor. METHODS AND RESULTS: All rabbits (n = 8) immunized with both peptides had a high titer of both anti-beta1-adrenoceptor and anti-M2-muscarinic receptor autoantibodies in their sera, whereas none of the sera from control rabbits injected with saline (n = 9) was positive. No significant cross-reaction with peptides other than those used for immunization was found. The weight of the hearts of immunized rabbits increased significantly. The hearts of immunized rabbits showed marked concentric left ventricular hypertrophy with mild inflammatory cell infiltration. In these rabbits, mild or moderate interstitial fibrosis was also observed. In electron micrographs, immunized rabbits showed focal myofibrillar lysis, loss of myofilament, and a marked increase in the number of mitochondria and deposition of dense granules in both sarcoplasm and myofibrils. Conversely, one of the control rabbits showed scant mononuclear cell infiltration. However, in this control rabbit, no significant alteration was found by electron microscopy. CONCLUSION: Our results showed the coexistence of both anti-beta1-adrenoceptor and anti-M2-muscarinic receptor autoantibodies in the sera has pathophysiological importance, shown by their ability to induce cardiac hypertrophy in rabbits.     

慢性心力衰竭患者心脏β1受体自身抗体与心功能的相关性及临床意义

目的 通过对慢性心力衰竭（心衰）患者血清中β1肾上腺素能受体自身抗体水平的监测,预测心功能情况,并指导β受体阻滞剂卡维地洛的临床应用。方法 65例心衰患者采用酶联免疫法测定患者血清中β1受体自身抗体水平,据此分为β1受体自身抗体阳性组（β1阳性组）30例和β1受体自身抗体阴性组（β1阴性组）35例,在血管紧张素转换酶抑制剂、利尿剂和洋地黄制剂治疗基础上加用β受体阻滞剂卡维地洛。随访半年,治疗前后采用超声心动图测量左室舒张末径（LVEDD）,左室收缩末径（LVESD）和左室射血分数（LVEF）进行比较。结果 （1）β1阳性组卡维地洛靶剂量明显高于β1阴性组[（36．25±14．31）mg／d与（25．97±8．83）mg／d],P〈0．01。（2）治疗前,p1阳性组心率显著高于p1阴性组[（94．19±14．46）次／min与（86．56±15．88）次／min],P〈0．05。治疗后,两组心率、血压均较治疗前显著减低（P〈0．01）,β1阳性组心率与β阴性组差异无统计学意义（P〉0．05）。（3）治疗前,β1阳性组LVEDD显著大于β1阴性组[（66．01±5．47）mm与（63．07±5．64）min],P〈0．05;LVESD大于β1阴性组[（54．24±8．43）mm与（50．72±6．12）min],P=0．052;LVEF显著低于β1阴性组[（32．16±9．00）％与（36．64±8．20）％],P〈0．05。治疗后,两组LVEDD、LVESD均较治疗前显著减小（P〈0．01）,LVEF较治疗前提高（P〈0．01）。β1阳性组LVEDD、LVESD和LYEF与β1阴性组差异无统计学意义（P〉0．05）。（4）β1阳性组治疗后血清中抗心脏β1受体自身抗体滴度较治疗前显著降低（1：119．35与1：72．21）,P〈0．01。结论 β1受体自身抗体参与心衰的病理生理过程,通过对β1受体自身抗体的检测可以预测患者的临床过程,提示对β1受体抗体阳性患者尽早使用β受体阻滞剂对于抑制心肌重构、改善心功能受益更大。     

Autoantibodies against the Beta- and Muscarinic Receptors in Cardiomyopathy

The sera of patients with idiopathic dilated cardiomyopathy and the Chagas' disease contain agonist-like autoantibodies directed against the beta 1-adrenoceptor and/or the muscarinic M2-receptor. The anti-beta 1-adrenoceptor antibodies could be directed against amino acid sequences of the first or second extracellular loop. In patients with dilated cardiomyopathy the first as well as the second extracellular loop was identified as an antibody epitope. In Chagas' disease the anti-beta 1-adrenoceptor antibody recognizes only 1 epitope on the second extracellular loop. The anti-beta 1-adrenoceptor antibodies acting like the beta-adrenergic agonist isoprenaline and exert a positive chronotropic effect in cultured rat cardiomyocytes. In contrast to isoprenaline the antibody caused no downregulation of the beta-adrenergic signal transduction cascade within 6 hours. The anti-M2 receptor antibodies recognize in both diseases an epitope on the second extracellular loop. The anti-M2-receptor antibody exert a negative chronotropic response in cultured cardiomyocytes. This antibody induced no downregulation of the muscarinic M2-receptor. The negative chronotropic effect was unabated for 6 hours. Based on these findings it is believed that the agonist-like autoantibodies that act against the beta 1-adrenoceptor and the muscarinic M2-receptor may play a role in the pathogenesis of dilated cardiomyopathy and Chagas' disease.     

beta(1)-Adrenergic receptor function, autoimmunity, and pathogenesis of dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a heart disease characterized by progressive depression of cardiac function and left ventricular dilatation of unknown etiology in the absence of coronary artery disease. Genetic causes and cardiotoxic substances account for about one third of the DCM cases, but the etiology of the remaining 60% to 70% is still unclear. Over the past two decades, evidence has accumulated continuously that functionally active antibodies or autoantibodies targeting cardiac beta(1)-adrenergic receptors (anti-beta(1)-AR antibodies) may play an important role in the initiation and/or clinical course of DCM. Recent experiments in rats indicate that such antibodies can actually cause DCM. This article reviews current knowledge and recent experimental and clinical findings focusing on the role of the beta(1)-adrenergic receptor as a self-antigen in the pathogenesis of DCM.     

Antigen-specific effects of autoantibodies against sarcolemmal Na-K-ATPase pump in immunized cardiomyopathic rabbits

OBJECTIVES: We examine antigen-specific actions of autoantibodies directed against sarcolemmal Na-K-ATPase. BACKGROUND: Autoantibodies against some receptors or pumps were detected in patients with dilated cardiomyopathy. Although immunoglobulin adsorption therapy improved cardiac function in such patients, direct pathogenic effects of autoantibodies remain to be proven. METHODS: Japanese white rabbits were immunized once a month with purified Na-K-ATPase (NKA rabbits, n=10) or a synthetic peptide corresponding to the second extracellular loop of beta1-adrenergic receptors (beta rabbits, n=10), respectively. Control rabbits (n=10) received vehicle in the same manner. RESULTS: At 6 months, cardiac hypertrophy along with increased left ventricular end-diastolic pressure was observed in both NKA and beta rabbits, and inhibitory G protein level increased in both NKA and beta rabbits. Histological findings showed similar myocyte hypertrophy and interstitial fibrosis in both rabbits. Enzymatic activities of Na-K-ATPase were lower in NKA rabbits than in other groups. Immunoblotting showed that alpha3-isoform of Na-K-ATPase was selectively reduced in myocardium from NKA rabbits. CONCLUSIONS: Our present findings suggested that isoform-specific alterations of myocardial Na-K-ATPase activity were induced by immunizing rabbits. This was not secondary change due to cardiac hypertrophy. Thus, autoantibodies against sarcolemmal Na-K-ATPase have antigen-specific effect on the heart in vivo.     

Polymorphism of the ADRB2 Gene and Response to Inhaled Beta- agonists in Children with Asthma: A Meta-analysis

Background. About 9% of children have asthma, corresponding to almost 6.8 million children in the USA and 1.1 million in the UK. Asthma exacerbations are the leading cause of pediatric emergency room visits and impose a large burden on the individual, family, and society. There is mounting evidence that therapeutic failure of inhaled beta-agonists is associated with polymorphisms of the β₂-adrenergic receptor gene (ADRB2); specifically, mutations leading to amino acid changes at positions 16 and 27, which alter down-regulation of the β₂-adrenergic receptor (β₂AR), induce resistance to the smooth-muscle relaxing effect of β₂-adrenergic agonists. Methods. We conducted a meta-analysis to examine the association between ADRB2 polymorphisms and the response to inhaled β₂-adrenergic agonists in children with asthma. We included all published studies until November 2008, in which asthmatic children underwent testing for acute bronchodilator response, defined as ≥ 15% improvement in forced expiratory volume in 1 second (FEV₁) and single nucleotide polymorphism (SNP) genotyping for positions 16 and/or 27 of the β₂AR. Individual and summary odds ratios were calculated using a random effects model. Results. We identified three case-control or family-based studies involving 960 asthmatic children (692 children with negative β₂-bronchodilator response, defined as < 15% improvement in FEV₁ and 268 children with positive bronchodilator response). We found a significant association between favorable therapeutic response to inhaled β₂-adrenergic agonists in asthmatic children and the Arg/Arg phenotype at position 16 of the β₂AR [OR = 1.77; 95% CI (1.01; 3.1); p = 0.029], compared with the Arg/Gly or Gly/Gly phenotypes. The beneficial effect of Arg at position 16 of the β₂AR was most pronounced in African-American asthmatic children [OR = 3.54; 95% CI (1.37, 9.13)]. There was no association between clinical response to β₂-agonists and polymorphism at amino acid position 27 of the β₂AR (OR = 1.04; 95% CI [0.76,1.42]). Conclusions. Failure of bronchodilator response to inhaled beta-agonists in asthmatic children is associated with the Gly allele (Arg/Gly and Gly/Gly genotypes) at position 16 of the β₂-adrenergic receptor. Genetic typing for β₂AR polymorphism may help identify children with drug-resistant asthma.     

Autoantibodies against the second extracellular loop of beta1-adrenergic receptors predict ventricular tachycardia and sudden death in patients with idiopathic dilated cardiomyopathy

OBJECTIVES: We sought to define the clinical and long-term prognostic implications of autoantibodies that act against the second extracellular loop of beta1-adrenergic receptors (ARs) in patients with idiopathic dilated cardiomyopathy (IDC). BACKGROUND: Although autoantibodies directed against various domains of beta-ARs are found in patients with IDC, only a subgroup against the second extracellular domain of beta1-ARs exerts intrinsic sympathomimetic-like actions on human beta-ARs. It is suggested that the autoantibodies take part in the pathophysiology of IDC and may affect long-term prognosis of patients with this disorder. METHODS: Sera from 104 patients with IDC were screened for autoantibodies that act against the second extracellular loop of beta1-ARs by enzyme-linked immunosorbent assay, using a synthetic peptide corresponding to the domain. Relations of the autoantibodies to clinical variables and long-term prognosis were assessed by multivariate analysis. RESULTS: Autoantibodies were detected in 40 patients (38%). Multifocal ventricular premature contractions (p < 0.01) and ventricular tachycardia (VT; p < 0.01) were more common in autoantibody-positive than in autoantibody-negative patients, although no differences in cardiac function or neurohormonal levels were demonstrated. The presence of autoantibodies (p = 0.001) and a low left ventricular ejection fraction (LVEF <30%; p = 0.02) were independent predictors of VT. Sudden death was independently predicted by the presence of autoantibodies (p = 0.03), as well as by LVEF <30% (p = 0.01), whereas total mortality was predicted only by LVEF <30% (p = 0.001). CONCLUSIONS: Autoantibodies directed against the second extracellular loop of beta1-ARs were closely related to serious ventricular arrhythmias in patients with IDC, and the presence of autoantibodies independently predicted sudden death. These autoantibodies may contribute to electrical instability in patients with IDC.     

免疫大鼠血清中抗β1、β3肾上腺素受体及M2乙酰胆碱受体抗体IgG亚类的分布

目的明确免疫大鼠血清中抗β1、β3肾上腺素受体及M2乙酰胆碱受体抗体的IgG亚类,为进一步研究此类抗体的作用机制提供实验依据。方法以合成的大鼠β1、β3肾上腺素受体和M2乙酰胆碱受体细胞外第二环肽段为抗原分别主动免疫Wistar大鼠,应用免疫球蛋白纯化技术特异性提纯其血清中IgG类抗体,应用BCA进行蛋白定量,调整血清中蛋白量一致,用SA—ELISA法检测抗β1、β3肾上腺素受体和M2乙酰胆碱受体抗体的IgG亚类。结果免疫组中属于IgG2a亚类的抗β1肾上腺素受体抗体的A值为（0．45±0．01）,明显高于对照组（0．08±0．003,P〈0．05）;免疫组中属于IgG2b亚类的抗艮肾上腺素受体抗体的A值为（0．59±0．02）,显著高于对照组（0．2±0．02,P〈0．05）;免疫组中属于IgG2a亚类的抗M2乙酰胆碱受体抗体的A值为（0．56±0．04）,显著高于对照组（0．12±0．01,P〈0．05）。结论免疫大鼠血清中抗β1肾上腺素受体抗体和抗M2乙酰胆碱受体抗体主要属于IgG2a亚类,抗β3肾上腺素受体抗体主要属于IgG2b亚类。     

IgGs and Mabs against the beta2-adrenoreceptor block A-V conduction in mouse hearts: A possible role in the pathogenesis of ventricular arrhythmias

Autoantibodies against beta-adrenoceptors might be involved in different cardiomyopathic diseases such as idopathic dilated cardiomyopathy, Chagas' disease and ventricular arrhythmias. To study the effects of such antibodies on the whole heart, we made use of a new technique allowing the measurement of Ca++ transients as well as action potentials in Langendorff preparations of mouse hearts. Mouse antibodies directed against the second extracellular loop of the beta2-adrenoceptor induced conduction blocks which could be washed away by the beta2-adrenoceptor inverse agonist ICI118,551, confirming the specificity and non-toxicity of these events. These results were confirmed by the use of a monoclonal antibody, monospecific for the beta2-adrenoceptor and the beta2-specific full agonist, clenbuterol. Both increased slightly, but significantly, the beating frequency but their main effect was the production of conduction blocks. In contrast, a monoclonal antibody, monospecific for the beta1-adrenoceptor, highly increased the beating frequency without interfering with the conduction. Our results suggest that stimulation of the beta2-adrenoceptor by anti-receptor antibodies in the conduction tissues leads to conduction disturbances, probably mediated by coupling to a different pathway than the classical Gs pathway. They confirm that anti-beta2 adrenoceptor antibodies could be responsible for ventricular arrhythmias.